1. Field of the Invention
This invention relates to asynchronous transfer mode networks and, more particularly, to a system and method for avoiding cell loss due to quality of service contract bandwidth usage constraints.
2. Description of the Related Art
The development of broadband integrated services digital networks (BISDN) based on asynchronous transfer mode (ATM) switching technology has the potential for ultimately replacing the plurality of existing networks presently required to carry voice, data, and video traffic. ATM is a high-speed packet switching technique employing short, fixed-length cells that are statistically multiplexed over virtual connections. Using ATM, different traffic types received in various user formats are segmented into fixed length cells that are transported to and reassembled into the original format at the destination node.
To achieve universality, standards and recommendations for service for ATM-based networks are promulgated by the International Telecommunications Union (ITU). In particular, the ITU-I Recommendation I.371 specifies a method for policing traffic through an ATM-based network via the use of traffic management contracts. A traffic contract is an agreement between an ATM user and the network provider regarding the quality of service (QoS) the ATM user can expect under specified conditions. The contracts are designed to ensure the integrity of information transport as well as an acceptable level of delay for voice and video traffic. One parameter specified in the traffic contract is the amount of guaranteed bandwidth. When a user exceeds the agreed-upon bandwidth, the excess cells are liable to be discarded if the network is congested. In order to ensure the integrity of data and information transport, users are therefore typically required to pay for a larger bandwidth allocation, which can be relatively expensive.
Accordingly, it is desirable to provide a system and method for ensuring cell integrity at optimal costs for QoS traffic contracts in ATM networks.